A multilevel converter is an electrical device comprising multiple modules designed in the same manner, each module having an associated voltage source of its own. During operation of the multilevel converter, multiple modules are combined with one another, a respective required resultant voltage being able to be produced from voltage sources of combined modules.
The document US 2013 0033 912 A1, which is incorporated by reference herein, describes a five-level converter having a capacitor set comprising two capacitors and two diodes, a switch and a full-bridge circuit. It is therefore possible for an AC voltage having precisely five voltage levels to be produced in this case.
The document US 2015 0009 734 A1, which is incorporated by reference herein, describes a method for controlling a mulitlevel half-bridge. The multilevel half-bridge in this case consists of two branches arranged symmetrically about a center tap and having an arbitrary number of switches. These switches are each connected to the corresponding switch of the other branch via a capacitor.
The document US 2015 0280 474 A1, which is incorporated by reference herein, describes a method for charging an energy storage device from a three-phase AC current source. In this case, each phase of the AC current source is connected to a step-down converter, a diode and a converter.
The document US 2015 0372 611 A1, which is incorporated by reference herein, describes a modular high-frequency converter having multiple submodules that each have a half-bridge and a full bridge, these being connected via a DC link circuit. A voltage measurement on the capacitance present in each DC link circuit allows the individual submodules to be selectively switched on or off in this way.
The document WO 2015/131931 A1, which is incorporated by reference herein, describes a multilevel converter having multiple submodules that consist of half-bridges and are interconnected either as a half-bridge or as a full bridge.
Against this background, an example provides a multilevel converter that includes multiple modules and a method for operating the multilevel converter. Magnetic fields induced when individual modules are switched on and off are intended to be reduced. Some examples include a module, a multilevel converter, and a method.
The module according to aspects of the invention is configured as a component of a multilevel converter and has multiple base units and electrical energy sources, each base unit having at least one half-bridge. The at least one half-bridge comprises at least one highside switch and at least one lowside switch. In this case, for two base units arranged directly adjacent to one another inside the module, there is provision for a first base unit to have the at least one highside switch connected to a positive pole of a first energy source and the at least one lowside switch connected to a negative pole of a second energy source, wherein a second base unit has the least one highside switch connected to a positive pole of the second energy source and the at least one lowside switch connected to a negative pole of the first energy source. During operation of the module, current is able to be transported between two poles via at least one current path.
Normally, the at least one current path is able to be connected between at least two directly adjacent switches.
In one configuration, the at least one current path is able to be connected for transporting current directly between the at least one highside switch and the at least one lowside switch of the at least one half-bridge, wherein the at least one current path is able to be used to transport current from the positive pole of the first or second energy source via the at least one highside switch and the at least one lowside switch to the negative pole of the second or first energy source.
Alternatively or additionally, the at least one current path is able to be connected for transporting current between a switch of the first base unit and a switch of the second base unit that are arranged directly adjacent to one another. Therefore, the at least one current path is connected directly between two highside, directly adjacent switches of two directly adjacent base units and/or directly between two lowside, directly adjacent switches of two directly adjacent base units. If the at least one current path connects two directly adjacent highside switches of the two base units, the current is transported from the positive pole of the first energy source via the two highside switches to the positive pole of the second energy source. If the at least one current path connects two directly adjacent lowside switches of the two base units, the current is transported from the negative pole of the first energy source via the two lowside switches to the negative pole of the second energy source.
At least one switch of the at least one half-bridge is configured as a semiconductor switch, for example as a transistor, as a metal oxide semiconductor field effect transistor (MOSFET) and/or as an insulated gate bipolar transistor (IGBT).
Each base unit comprises a positive busbar and a negative busbar, wherein the at least one highside switch of the at least one half-bridge is connected to the positive busbar and the at least one lowside switch of the at least one half-bridge is connected to the negative busbar. The two base units arranged directly adjacent inside the module, there is provision for the first base unit to have the positive busbar connected to the positive pole of the first energy source and the negative busbar connected to the negative pole of the second energy source. Moreover, the second base unit has the positive busbar connected to the positive pole of the second energy source and the negative busbar connected to the negative pole of the first energy source.
At least one electrical energy source of the module is configured as a voltage source, normally as a DC voltage source, for example as a battery or storage battery and/or capacitor.
Moreover, the base units are arranged on a circuit board. Therefore, the base units are arranged beside one another on the circuit board. Normally, each base unit comprises a housing enclosing the switches. Switches from two directly adjacent base units arranged directly beside one another are separated from one another only by the housings of the two base units.
The multilevel converter according to aspects of the invention has multiple modules, wherein each module has multiple base units and electrical energy sources, wherein each base unit has at least one half-bridge, wherein the at least one half-bridge comprises at least one highside switch and at least one lowside switch. For two base units arranged directly adjacent to one another inside the module, there is provision for a first base unit to have the at least one highside switch connected to a positive pole of a first energy source and the at least one lowside switch connected to a negative pole of a second energy source, wherein a second base unit has the at least one highside switch connected to a positive pole of the second energy source and the at least one lowside switch connected to a negative pole of the first energy source. In this case, current is able to be transported between two poles via at least one current path.
In the multilevel converter, all of the modules are configured equally or in the same manner and/or similarly. During operation of the multilevel converter, at least one module is active. If multiple modules are active at the same time, these modules are able to be connected in series with one another or in parallel with one another. The multilevel converter is configured as an energy source for an electrical machine.
Additionally, there is provision for the multilevel converter to be arranged in an electrical energy network of a motor vehicle. The multilevel converter can be used to supply an electrical machine, for example, with electric power. The electrical machine is able to be operated as a motor and/or as a generator and being configured to drive the motor vehicle. The multilevel converter has at least one embodiment of the module.
The method according to aspects of the invention is provided for operating a multilevel converter having multiple modules as components. In this case, each module has multiple base units and electrical energy sources, wherein each base unit has at least one half-bridge, wherein the at least one half-bridge comprises at least one highside switch and at least one lowside switch. For two base units arranged directly adjacently to one another inside the module, there is provision for a first base unit of the two base units to have the at least one highside switch connected to a positive pole of a first energy source and the at least one lowside switch connected to a negative pole of a second energy source, and wherein a second base unit of the two base units has the at least one highside switch connected to a positive pole of the second energy source and the at least one lowside switch connected to a negative pole of the first energy source. Current is transported between two poles via at least one current path.
In one configuration, the at least one current path for transporting current is connected directly between the at least one highside switch and the at least one lowside switch of the at least one half-bridge, wherein the at least one current path is used to transport current from the positive pole of the first or second energy source via the at least one highside switch and the at least one lowside switch to the negative pole of the second or first energy source.
In a complementary or alternative configuration, the at least one current path for transporting current is connected directly between a switch of the first base unit and the switch of the second base unit that are arranged directly adjacent to one another. Therefore, the at least one current path is connected directly between two highside, directly adjacent switches of two directly adjacent base units and/or directly between two lowside, directly adjacent switches of two directly adjacent base units. If the at least one as current path connects two directly adjacent highside switches of the two base units, the current is transported from the positive pole of the first energy source via the two highside switches to the positive pole of the second energy source. If the at least one current path connects two directly adjacent lowside switches of the two base units, the current is transported from the negative pole of the first energy source via the two lowside switches to the negative pole of the second energy source.
Moreover, each module provides an output voltage, wherein at least two modules are connected in series with one another and/or in parallel with one another, a combined and/or resultant output voltage being provided for the multilevel converter from the output voltages of the modules combined with one another or connected in parallel and/or in series with one another.
Normally, current is transported by at least one first current path, wherein a commutation or switching of a respective module results in the at least one first current path being deactivated or switched off and at least one second current path being activated or switched on, the current being transported by the at least one second current path after the commutation.
The multilevel converter is configured for producing an AC voltage from multiple DC voltages, inter alia, and, in one configuration, comprises multiple modules connected in series, each module in turn comprising four MOSFET half-bridges and two voltage sources. Each MOSFET half-bridge has a high side and a low side comprising in each case four highside and lowside switches, for example transistors, wherein additionally two respective MOSFET half-bridges are connected to one another. Switching the current paths between the connected MOSFET half-bridges produces a required AC voltage.
In one configuration, there is provision for the various current paths connected between directly adjacent switches in a base unit or between two base units or across base units to overlap and also be short. Therefore, only low inductances build up in the event of a switching, as a result of which overvoltages are avoided and switches, for example transistors, are protected against damage. Additionally, the envisaged topology of a circuit of the multilevel converter means that the various switches, for example transistors, on one side, i.e. the highside switches or the lowside switches of a half-bridge, are loaded evenly, since there are current paths of the same or similar length for the transistors.
In the envisaged topology of the multilevel converter, the low and high sides of two connected half-bridges are interchanged with one another. Moreover, the two half-bridges are interlaced with one another. As a result of this topology, the various current paths overlap at least partially and are distinctly shortened, reducing inductances that arise during switching. Additionally, the length of the current path is also the same for each switch, which means that all subassemblies configured as switches are loaded equally.
Usually, the multilevel converter according to aspects of the invention comprises multiple modules, wherein each of these modules in turn has multiple base units and multiple energy sources, usually voltage sources, configured as batteries or capacitors. During operation of the multilevel converter, at least one of the modules is able to be activated. If multiple modules are activated, they are connected in parallel and/or in series with one another, as a result of which the multilevel converter is able to be used to provide different voltages having different maximum values and/or amplitudes as required.
Each base unit comprises multiple half-bridges, wherein in each case a highside switch and a lowside switch inside a base unit are arranged directly adjacent to one another. If the module has two voltage sources, for example, there is provision for highside switches of a first base unit to be connected to the positive pole of the first voltage source, whereas the lowside switches are connected to the negative pole of the second voltage source. Moreover, the highside switches of the second base unit are connected to the positive pole of the second voltage source and the lowside switches are connected to the negative pole of the first voltage source. In this case, these two base units are likewise arranged directly adjacent to one another.
On the basis of such a layout of the base units, comparatively short current paths arise between two switches. When switching between two operating states or in the event of a commutation of the base unit, however, only currents along short current paths are built up and dissipated again, but with only comparatively small magnetic fields being induced that impair operation of the subassemblies only slightly. The base units of the modules of the multilevel converter that are connected in series, for example, allow rapid switching of the current paths. If multiple modules and/or base units are connected in succession, it is additionally possible to provide an AC voltage from a DC voltage from voltages sources of the modules.